Aircraft have flight control devices on the leading and/or trailing edges of their aerofoil sections, such as the wings, horizontal tailplane, and vertical tailplane. Common leading or trailing edge devices are slats, flaps, spoilers, ailerons, elevators, rudders and air brakes. These flight control devices typically operate to provide enhanced lift or drag during low speed flight, for example take-off/climb and landing/descent, or to provide pitch, roll and yaw control during any of the flight phases.
When some of these flight control devices are deployed, a void is opened up in the upper and/or lower aerodynamic surfaces of the respective aerofoil section. It can be highly undesirable for an air path to be created between the lower and upper aerodynamic surfaces, as high pressure uplift air on the lower surface may leak through to the low pressure upper surface, which will impact upon the lift performance of the aerofoil. Also, voids created in the upper and lower surfaces cause surface discontinuities which leads to an increase in parasitic drag, noise etc. It is therefore desirable to seal these voids.
Aircraft wing trailing edge flaps are high lift devices which are typically deployed on take-off and landing to increase the lift coefficient by increasing the camber of the wing aerofoil. This is achieved by rotating the flap downwardly about its hinge line with respect to the main wing aerofoil portion. Some flaps, for example the Fowler flap, further increase the lift generated by the wing by also increasing the planform area of the wing. This is achieved by translating the flap aft as the flap is rotated downwardly. A “drop hinge flap” is a further type of flap which translates downwardly with respect to the main wing aerofoil portion as it rotates downwardly, when deployed.
Spoilers are flight control devices which are typically rotated upwardly from the aircraft wing trailing edge into the airflow to spoil the airflow and hence reduce the lift generated by the wing aerofoil. Spoilers are typically mounted spanwise between the main wing aerofoil portion and some of the flaps. The spoilers, when not deployed upwardly, provide a continuous upper surface of the wing between the main aerofoil portion and the flaps. However, spoilers are generally not provided across as much of the wing span as the flaps and so panels are provided spanwise between the main aerofoil portion and the flaps in regions not occupied by spoilers.
The drop hinge flap creates an effective slot between the trailing edge of the spoiler and the leading edge of the flap when deployed. This slot can further enhance the lift performance of the drop hinge flap. However, if this slot is too large and the continuity of the upper aerodynamic surface is not maintained, then the performance of the drop hinge flap is not as good as the Fowler flap. To control the size of the slot, the spoilers and the panels between the main aerofoil portion and the flaps are rotated downwardly or “drooped” when the drop hinge flaps are deployed.
On conventional, non-drooping spoilers, a seal is typically provided to sit beneath the leading edge of the spoiler. FIG. 7 shows a conventional spoiler seal 100 fastened to a wing trailing edge upper cover 200, and which contacts a leading edge of a spoiler 300. When the spoiler 300 is deployed upwardly, the spoiler will lift away from the seal 100 in the direction of arrow D. It is generally not necessary to seal the spoiler when it is deployed upwardly. When the spoiler 300 is in its neutral, i.e. not deployed position, as shown in FIG. 7, it is highly desirable to prevent cross-bleed air from passing from the lower wing surface, due to e.g. flap deployment, to the upper wing surface between the wing trailing edge upper cover 200 and the spoiler 300. By providing the seal 100 beneath the leading edge of the spoiler, the high pressure air from the lower surface will force the seal tight against the leading edge of the spoiler preventing cross-bleed. Panels disposed spanwise between non-drooping spoilers are generally fixed as they are required to neither droop nor be deployed upwardly into the airflow. The sealing of such panels is therefore trivial.
For drooping spoilers and drooping panels, the sealing at the spoiler or panel leading edge becomes more difficult. Not only does it become necessary for the panels to be sealed as well as the spoilers, but the seal 100 shown in FIG. 7 cannot be used as it would become damaged as the spoiler/panel droops. A seal instead has to be provided to seal against the upper (rather than lower) surface of the spoiler or panel. However, there is nothing for the seal to act against to prevent the high pressure air pushing through to the upper surface. This can cause the seal to flutter and a cross-bleed of air from the lower to the upper surface of the wing can occur.
This problem is not restricted to drooping spoiler/panel assemblies and could be found in any aircraft flight control device that is not part of a closed “box”, i.e. it is (temporarily) exposed to airflow from beneath and is only sealed from above. By contrast, most ailerons have two seals, one on the upper and one on the lower surface at the aileron leading edge, to form a closed “box”, such that no void is created when the aileron is deployed upwardly or downwardly from its neutral position.